Summer and Autumn Activity of Eptesicus nilssonii and Other Bat Species in a High-Altitude Ice Cave in the Tatra Mountains (Southern Poland)

The aim of this study was to examine the role of a high-elevation ice cave (Lodowa Cave in Ciemniak, Mt. Ciemniak, 1715 m a.s.l., Tatra Mountains, Poland) in the seasonal and nightly activity of bats. Bat activity was monitored using mist-netting and direct observations during the summer and autumn seasons of 2008-2011 and 2021. A total of 723 bats representing 10 of the 28 species known from Poland were captured. <i>Eptesicus nilssonii</i> predominated (57.5% of the total) and exhibited consistently high activity throughout the study period. Males predominated in almost all species, with <i>E. nilssonii</i> showing a strong male bias (85%), while adults were dominant and juveniles were rare (only 1.2% in <i>E. nilssonii</i>). Species composition and abundance varied seasonally, and swarming activity occurred between June and November, with a clear peak in July and August. Activity patterns were species-specific: <i>E. nilssonii</i> showed a pronounced peak approximately two hours after sunset, while <i>M. mystacinus</i> and <i>P. auritus</i> displayed distinct temporal activity profiles. A copulating pair of <i>E. nilssonii</i> was recorded in September 2011. Our findings suggest that high-altitude ice caves serve as key summer and autumn swarming and mating sites for <i>E. nilssonii</i>, highlighting their ecological importance in a warming climate.